1. Field of the Invention
The present invention relates to the installation of pipelines in a marine environment, and more particularly relates to an apparatus which supportably receives a pipeline after construction on a lay barge and supportably guides the pipeline to the ocean floor where the pipeline is then deposited continuously into a ditch which is continuously plowed and cleaned by the device during the laying operation.
2. General Background and Prior Art
Pipelines are required for the transmission of many products in our industrial society. Generally such products are fluid, but can be any flowable matter such as slurries and the like.
Pipelines have been used extensively in the transmission of products across a marine environment where other types of transportation would be impossible, highly expensive or not adequate to carry sufficient quantities. This is true of many products mined offshore which are not easily confineable and thus are especially suited to transmission through pipelines, for example, petroleum products, gas, oil and the like.
It is to this general field that the present invention is directed.
An offshore pipeline is widely used to transmit petroleum products and the like from offshore oil and gas fields inward, to consumer markets. Construction can be very costly as the marine environment is a difficult environment in which to construct anything. In fact, most offshore oil rigs are constructed inland and set in place after completely built, by hugh derrick barges. This procedure is not possible with pipelines which are not structurally sound enough to be totally built on land and thereafter laid in place. On some lines of relatively short length, they can be constructed onshore and pulled offshore through a ditch into place, but in the majority of marine installations, fabrication onsite is required. The "pulling" of a pipeline is also adjacent feasible where bottom sediment conditions cause any constructed ditch to rapidly fill in.
The installation of pipelines in a marine environment generally utilizes a barge structure known as a "lay barge" on which welders and like workmen construct the pipeline joint by joint and continuously feed the welded line off the end portion of the lay barge towards the ocean floor where it rests to be buried by natural sedimentation. Joints are usually relatively short (a 40 foot joint being typical). Thus joints can easily be stacked and sequentially welded tip to tip as the pipeline is lowered toward the ocean floor off the tail end of the barge. Thereafter, a second rig drags a "jet sled" along the line to bury the line in place. A ditch is prepared by the sled which the sled usually digs as it is propelled along the pipeline, either by gripping the line itself or by means of a vessel which imparts necessary tension to the sled to give it forward motion.
This method is extremely costly, complex and time consuming. When a jet sled is required to both dig the trench and bury the line after expenses have already been incurred to lay the line on the bottom, a great deal of unnecessary expense arises in the cost of construction which must ultimately be borne by the consumer in the form of higher fuel costs.
Several devices have been patented which have attempted to solve the problem of constructing and burying pipelines in the marine environment.
The devices usually require some mechanism to remove soil or sediment in order to form a ditch, and often a second mechanism to clean the ditch and prevent sedimentation back into the ditch.
The following table lists a number of prior art devices which have been patented, which devices utilize some type of plow to assist in forming an excavation into which a pipe or cable will be placed in a marine environment.
______________________________________ PRIOR ART PATENTS USING A PLOW STRUCTURE U.S. Pat. No. INVENTOR(S) ISSUE DATE ______________________________________ 2,693,085 I. S. Salnikov Nov. 2, 1954 2,795,111 L. W. Richardson June 11, 1957 2,875,585 T. R. Little Mar. 3, 1959 2,992,537 L. Callahan July 18, 1961 3,339,368 Takuji Ezoe et al Sept. 5, 1967 3,368,358 H. A. Elliott Feb. 13, 1968 3,504,504 H. A. Elliott Apr. 7, 1970 3,540,226 B. L. Sherrod Nov. 17, 1970 3,641,780 A. N. Ede Feb. 15, 1972 3,824,798 K. Shiroyama, et al July 23, 1974 ______________________________________
The following table lists other ditching marine devices which have been patented.
______________________________________ PRIOR ART PATENTS U.S. Pat. No. INVENTOR(S) ISSUE DATE ______________________________________ 3,103,790 N. P. Popich Sept. 17, 1963 3,217,499 I. Ishiki Nov. 16, 1965 3,333,432 A. L. Hale et al Aug. 1, 1967 3,338,059 J. G. Tittle Aug. 29, 1967 3,423,946 J. C. Maclay Jan. 28, 1969 3,429,131 C. F. Martin Feb. 25, 1969 3,507,345 D. R. Vaughan et al Apr. 21, 1970 3,576,111 U. A. Henry, Jr. Apr. 27, 1971 3,717,003 H. J. Bates, et al Feb. 20, 1973 3,722,224 L. H. Roy Mar. 27, 1973 3,732,700 R. P. Lynch May 15, 1973 3,751,927 J. C. Perot, Jr. Aug. 14, 1973 3,786,642 A. E. Good, et al Jan. 22, 1974 3,803,856 F. Galdi Apr. 16, 1974 3,877,237 R. M. Norman Apr. 15, 1975 3,877,238 N. M. Chang, et al Apr. 15, 1975 3,898,852 Takuji Ezoe, et al Aug. 12, 1975 3,926,003 R. M. Norman Dec. 16, 1975 ______________________________________
In most of the prior art patents which use a "plow", the plow structure straddles the pipe, the pipe having been prelaid on the ocean floor. The Sherrod U.S. Pat. No. 3,540,226, however, receives the pipe directly from the barge and lays it in a formed trench in the same operation. However, Sherrod teaches the use of an extensive, bulky "ballast train" for support of the pipeline. Such a ballast train is not required with the present invention, as the pipeline receives substantially all its support from the vertical supports provided on the structural frame portion of the sled itself. Such a ballast train would be undesirable in deep water or water with heavy currents in which control of such a ballast train would be impossible.
Devices of the prior art are for the most part complex, expensive, and awkward. Many have the major drawback of entirely too many moving parts to be useable in an underwater environment which is both corrosive and abusive to equipment. In addition to having an excessive number of moving parts, many prior art devices require excessive energy to power various scrapers, augers, blasting nozzles, and the like which actually perform the trenching operation. The cleansing system used with each device to sweep the plowed ditch and keep it free of sediment is often comprised of expensive and power consuming pumps, eductors, and like sophisticated fluid moving devices. While these devices may in fact be successful in keeping the ditch clean of sediment, they are quite costly to operate and in their complexity often require a longer period of time to do the required job.